This invention relates to techniques for the manufacturing of flexible metal tubing capable of withstanding substantial pressures and the metal tubing made thereby and more particularly to a process and apparatus for manufacturing metal tubing which comprises a plurality of thin walled layers concentrically formed and subsequently corrugated.
Metal tubing capable of withstanding substantial pressures is required for applications involving the direct transportation of liquid and gaseous media as well as the sheathing of electric cabling or heat insulated coaxial conductors. Furthermore, since gaseous pressurized insulating media are frequently employed in electric cabling and heat insulated coaxial conductors to provide appropriate insulation, the tubing employed in the formation of such cabling or conductors is frequently exposed to considerable pressure as generated both from internal and external sources which must be withstood for the appropriate maintenance of acceptable operational characteristics. For instance, in deep sea drilling or well logging applications presently taking place, metal sheathed power cabling is frequently employed and the metal tubing relied upon to form the metal sheath must be able to withstand the substantial ambient pressure loads which manifest themselves during such applications. For instance, at depths of 4,000 meters, the metal tubes employed to sheath power cabling must be able to withstand pressures in excess of 400 atmospheres.
Conventional techniques for the manufacture of metal tubing capable of withstanding pressures of the type encountered in deep sea drilling applications and the like, as aforesaid, are disclosed for instance, in German DT-OS2 019 362. However, the resulting plain tubing set forth therein is highly specialized in nature and can only be formed in relatively short lengths because of its rigidity. Thus, in use, tubing of this nature is both expensive and time-consuming to employ because a large number of specialized fittings are required to join adjacent sections together into a resulting configuration which is capable of withstanding substantial pressures. Furthermore, if plain metal tubing whose wall thickness has been built up to withstand anticipated pressures is considered, it will be appreciated by those of ordinary skill in the art that the same is rigid in nature and may not be corrugated by conventional techniques as known forms of corrugator discs cannot withstand the pressure loads generated by such thick walled tubes. Thus even with plain tubing purposely thickened to withstand high pressure loads, flexibility is not a readily available characteristic and hence the manufacturing thereof in continuous lengths is generally precluded.
The instant invention proceeds from the dual discovery that concentrically formed thin walled metal tubes are capable of withstanding pressures equal to or greater than those withstood by individual thick walled metal tubes and that such concentrically formed thin walled metal tubes may be corrugated by substantially the same corrugation techniques employed for the corrugation of a single thin walled metal tube or sheath when the concentrically arranged tubes are formed in accordance with the teachings of the instant invention. The resulting corrugated structure may be manufactured on a continuous basis and hence, the length of the continuously formed metal tubing manufactured in accordance with the teachings of the instant invention is only limited by the amount of corrugated metal tubing which may be wound on one or more take-up reels. Furthermore, the flexible metal tubing formed in accordance with the teachings of the instant invention completely avoids the rigidity and multitudinous couplings and transitions associated with the use of thick walled tubing previously thought to be necessary for high pressure applications by the use of a plurality of concentrically formed thin walled tubes, while relying upon corrugation techniques which have been previously utilized to enhance the flexibility of cable and the like but only under such conditions where thin walled single element metal tubes were employed. Accordingly, the novel manufacturing techniques taught by the instant invention yield a resulting structure which is flexible and available in continuous lengths. This is achieved by certain manufacturing techniques usually employed to accomplish the cost reduction associated with the use of thin walled structures, while overcoming a previously thought to exist, art recognized limitation in the use of corrugation techniques to singular thin walled structures.
Therefore it is a principle object of the instant invention to provide a process and apparatus for manufacturing flexible metal tubing in extended lengths which is capable of withstanding substantial pressures as well as the metal tubing made thereby. Other objects and advantages of the present invention will become clear from the following detailed description of an exemplary embodiment thereof, and the novel features will be particularly pointed out in conjunction with the claims appended hereto.
In accordance with the teachings of the instant invention, manufacturing techniques for the formation of extended lengths of flexible metal tubing capable of withstanding substantial pressures are provided wherein a plurality of metal tubes are concentrically formed one about the other; each metal tube formed, after the first, is immediately drawn down to a desired diameter so that a resultant structure comprising a plurality of thin walled concentrically formed tubes is achieved; after all of the tubes in the desired structure have been formed, the resultant structure is corrugated in a transverse-axial direction to render the resultant structure formed flexible. Thus, the flexible metal tubes made in accordance with the teachings of the instant invention may be wound on take-up reels and hence produced according to continuous or endless manufacturing techniques to thus avoid the multitudinous couplings and transitions required by high pressure, rigid cable heretofore available in the prior art.